It is generally recognized that the amount of organic material in the form of BOD (biological oxygen demand), COD (chemical oxygen demand), and color bodies currently being discharged into public water supplies from pulp and paper mills is a problem of increasing importance in water pollution.
In the manufacture of paper, cellulose from both hard woods and soft woods is converted to pulp by various processes such as the sulfite process and the sulfate process and the pulp is subjected to various treatments particularly bleaching which involve the use of chemical reagents such as chlorine, chlorine dioxide, sodium hypochlorite and caustic alkalis. As a result of these treatments, the paper making process produces highly colored effluents. The bleaching of the pulp, in particular the caustic extract effluent is a major contributor to pollution problems.
Lignin is a primary source of color in the pulp. Chlorination of the pulp during the bleaching operation results in the formation of color bodies which are leached from the pulp by caustic alkali solutions. Thus, the caustic extract effluent contains a major proportion of the color bodies and other organic materials which have to be disposed of in waste water treatment.
Several processes are now used or advocated for use in removing color from paper mill waste. One of these is the so-called "massive lime process". This process utilizes lime in quantities ranging from 5,000 to 20,000 parts per million (ppm) to remove by coagulation and sedimentation techniques the organic colored bodies from paper mill wastes.
Another process that has been proposed is the use of organic solvent solutions of water insoluble amines as extractants for color bodies from paper mill waste water. Each of these processes has one or more objections which it would be desirable to eliminate.